The present invention relates to a semiconductor laser structure and, more particularly, to a semiconductor laser array which includes a plurality of active wave guides.
A semiconductor laser has been widely used as a light source in optical information processing systems such as an optical disc system a laser printer, and a medical apparatus.
However, the conventional semiconductor laser has merely a single active wave guide structure. Therefore, the maximum output of the laser in practice is about 60 to 70 mW.
Recently, to enhance the output level, a semiconductor laser having a plurality of active wave guides has been developed. The active wave guides are optically phase coupled to each other so as to emit the laser beam in a single phase. In other words, the laser beam from the adjacent two laser emitting regions is coupled so as to synchronize optical phases. This is referred to as the phase coupled laser array.
For example, W. Streifer et al of XEROX Corporation proposed a semiconductor laser array having ten active wave guides. (Appl. Phys. Letters, 42495 (1983)) The proposed laser array has, it has been reported, up to an output power of 200 mW, the device having a half value and full width less than 2 degrees in a far field pattern. In this laser structure, the beam output in the vertical mode from each of active wave guides are different from one another. Therefore, the beam phase from the active wave guides can not be synchronized with the other beam phases.
Another laser structure has a plurality of active wave guides in parallel in which the laser beams from the active wave guides are coupled by using a leak beam from each of the active wave guides. But, the above problem described in the first example still occurs. At the same time, in the above structure, the adjacent two active wave guides are coupled with polarizing action in crystallization like a wave guide type directional coupler. Therefore, the electric field has a phase difference of 180 degrees at the adjacent two active guides. The far field pattern has two peaks as shown in FIG. 4. In this situation, the optical system is not used to concentrate rays of light into a focus.